Using both hamster fetal cells and the 3T10 1/2 mouse cell line from Dr. Charles Heidelberger's laboratory, we shall look at the cell cycle specificity of malignant transformation with ara-C, FUdR, hydroxyurea, 5-azacytidine, Vincristine, Vinblastine, colchicine and other drugs. A possible common mechanism for malignant transformation with these agents will be studied. The hypothesis that there are specific chromosomes responsible for the expression of malignancy in chemically transformed hamster fetal cells will be tested. Various ara-C transformed clones and their revertants will be also studied for their chromosome complement and C- type RNA virus production. We shall attempt to show on which chromosome(s) the genes for the expression of C-type RNA virus are located in hamster cells.